Bioelectrical activity in temporalis and masseter muscles across different gnathic types

Relevance. Discrepancies in the bioelectrical activity of the masseter muscle were observed through surface electromyography analysis. Despite the availability of scientific literature on the morphological and anatomical variances in the mastication muscles and subcutaneous adipose tissue across different gnathic types, these differences are often overlooked in the interpretation of surface electromyography absolute values.

Materials and methods. A clinical evaluation, including the measurement of craniofacial parameters and an electromyography study of the right and left temporalis (RTA and LTA) and masseter muscles (RM and LM), was conducted on 73 individuals aged 21 to 24. Subjects were categorized based on upper and lower face gnathic type indices into three groups of 10: Group 1 (brachyfacial type), Group 2 (mesofacial type), and Group 3 (dolichofacial type). The study compared the surface electromyography-derived IMPACT index and average amplitude values of the muscles across groups, alongside analyzing the correlation between electromyographic values and gnathic type indices (GPDu.f./t-t and GPDl.f./ko-ko), with statistically significant differences noted at p ≤ 0.017.

Results. Differences in RM and LM parameters, and the IMPACT index during the "Maximal Voluntary Gnathic Clenching of the Jaws" (MVC) test were statistically significant among the groups. An increase in both the IMPACT index and average masseter muscle values was noted in dolichofacial subjects. Significant variations in LM values during the MVC test were observed between dolichofacial and mesofacial subjects. In the MVC test, groups 1 and 3 demonstrated a moderately strong positive correlation between the IMPACT index and GPDu.f./t-t and GPDl.f./ko-ko, while a strong positive correlation was identified between the RM parameter and GPDu.f./t-t and GPDl.f./ko-ko.

Conclusion. In the MVC test, the RM and LM parameters, as well as the average IMPACT index, were notably higher in dolichofacial subjects compared to other groups. A direct correlation between the mean right masseter bioelectrical activity and the average IMPACT index with the upper and lower facial gnathic indices was observed in brachyfacial and dolichofacial subjects in the MVC test.

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